Process for manufacturing composite board



Patented May 26, g 1953 'uNITEo sTATEsrArENT OFFICE N Drawing.Application July 26, 1948, Serial No. 40,791

1 Claim. 1

This invention relates to the manufacture of composite boards fromparticled ligneous material such as wood-shavings, coarse sander-dust,or mechanically-defibered wood; the customary procedure being to mix thematerial with a suit able binder and subject it to heat and pressure ina board-mold.

Most varieties of wood, other than those of the coniferous type havinghigh rosin-content, require the addition of a cementitious binder forthe production of a board having even only little strength or modulus ofrupture; the added binder usually being a substance such as a syntheticresin which materially increases the manufac turing cost. With woods ofthe non-resinous variety it has heretofore been proposed to employ as abinder the lignin which constitutes the essential part of all ligneoustissue but which is inert except during the life of the tree andtherefore must be liberated or reactivated before it can serve as thebinder. Liberation of the lignin can conveniently be effected by theprocess of hydrolysis in the presence of :a catalytic agent such as anacid. However, this process, as heretofore carried out, has been costlyfrom the standpoint of time and labor since it involved (1) prolongedheat-treatment, (2) separation of liquid, and usually (3) separation ofsubstances added to influence the hydrolytic actionbefore the activatedlignin, or the woody material containing such lignin, was available foruse in the actual pressing of the composite board.

It is therefore an object of my present invention to simplify, and torender less expensive, the manufacture of composite board; this objectbeing accomplished by the process hereinafter described and moreparticularly defined in the appended claim.

According to this invention :a composite board, having sufficientstrength for many purposes, can be produced in the following manner: Tothe ligneous material, which conveniently may be in the form ofshavings, coarse sander-dust, or mechanically-defibered wood, is addedwater to increase the normal moisture-content of the material to about15 to 30 per cent by weight. The moist material is then sprayed with adilute solution of an acid such as hydrochloric or sulphuric; theproportion of acid (as represented in concentrated state) to the totalweight of the mixture being /3 to 2 per cent. The acidified material isthen placed in a conventional board-mold and subjected to moderate heat(275-350 F.) and pressure (conveniently, 50 pounds per square inch) forabout 6' to 10 minutes; the board being in finished condition when it isthen removed from the mold.

The moisture content of the mixture may lie in an even narrower rangethan that indicated above, since it has been found by some tests thatwith a moisture content of 20 to 25 per cent a desirable balance isachieved between (1) the time necessary to dissipate the excess moisturein the heated mold, and (2) the beneficial effects of the moisture insoftening the fibers and thereby so increasing the liberation of ligninby the acid that the final density of the board under any chosenpressure is increased.

The acid is employed in diluted form so as to more readily and fullyefiect its dispersion throughout the mixture. It has been found that thebest results :are obtained when the amount of acid is within the/2-130-2 per cent range mentioned; the lower the acid content the lessis the danger of burning or darkening the board, while with the higheracid-content there is a greater release of lignin and resultant strongerboard. Hydrochloric acid is preferred since it volatilizes readily underthe heat and thus penetrates the fibers thoroughly; however, otheracids, notably, sulphuric, may be employed if due precautions are takenin handling it, and if darkening of the product (as may occur due to itsuse) is not objectionable.

According to my invention it is not necessary to employ any binder inaddition to that afforded by the lignin liberted in the process.However, to meet certain strength requirements synthetic binders may beadded either during the process, or subsequent to the removal of theboard from the mold, as by dipping the board in a conventional bindersolution and then redrying it. If added to the acidified mixture priorto pressing, the binder may be such as a commercially-obtainablethermo-setting resin of the phenol type. A strong-er product can also beobtained by the use, in addition to the acid, of a catalytic substancesuch as phenol to increase the liberation of lignin. It is to beunderstood that the use of additional binders or catalysts are notnecessary in the practice of my invention, and that their use (to meetgreater strength requirements) is to be considered as a step merelyadditional to those of the invention as claimed.

From the foregoing it is apparent that, by my improved process,composite boards can be produced directly from the basic ligneousmaterial merely by the addition of a small amount of water and acid, andthat no equipment other than the standard board moid and press isrequired.

I claim:

A process for manufacturing composite board from particled driedligneous material which consists in spraying the particied driedIigneous material with diluted hydrochloric acid in an amount such thatthe-acid, asrepresented in own-- centratd state, is ih theproiuoitibE-bfibn'e half to two per cent of the total weight of thematerial and the moisture content of said partici'efl dried li'gneousmaterial is brought to about twenty to twenty-five percent by weight,"

mixture in a mold and therein subjectiffi'i't 'to a temperature of275-350 F. to eifefit -10 4 lignin by said acid, and at the same time toa. pressure suflicient to compound the material into a finished board.

WINFRED E. WILSON.

References Cited in the file of this patent UNITED STATES PATENTS UTHER,REFERENCES hemistry--W1se, 1944-Da

